PARKINSONISM, described in its entirety over one hundred and fifty years ago,’rarely presents itself as a diagnostic problem. In consequence, little scrutiny has been directed to the marked variability of this frequently encountered neurological syndrome and to the progression of the disease in large groups of patients. As with most chronic neurological disorders, marked diversity can be expected to exist in age and mode of onset, relative prominence of the cardinal signs and symptoms, rate of progression, and resultant degree of functional impairment. Controversy over the effectiveness of therapeutic measures for parkinsonism is due partially to this wide variability and to the paucity of clinical information about the natural history of the syndrome. It is also re-